Overheat coolant - SD25 D21 1987 Nissan

SD diesels were widely available in the US in the 1981-86 Datsun/Nissan 720 pickups, and in Canada through '87 in the D21 pickup.

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after oil
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Location: powell river, BC, Cascadia

Overheat coolant - SD25 D21 1987 Nissan

#1

Post by after oil » 13 years ago

thermometer off the scale last night after driving only a few minutes in cold weather. pulled over and discovered empty rad! i filled it and drove 15km home. i blasted the heaters, only cold came out. the engine was cold to the touch. if i turned off the heater, the thermometer goes to H.
filled the rad again this morning, and after a few minutes i could see the rad's resevoir filling then overflowing.
i took off and tested the thermostat (broke a bolt off inside the housing, dang!) and heated it up in water on the stove and it appears to be working fine.
am i in serious trouble or what?

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philip
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Re: overheating but feels cold, thermostat ok

#2

Post by philip » 13 years ago

"after oil" ..

Too much going on all at once.

So cover the mechanical basics and start over.

You're looking for external coolant leaks (pump, hoses, radiator top/bottom, freeze plugs, heater core, etc) once the engine is up to temperature and coolant pressurized.

Temperature gauge fault. Reads high due to chaffed sender wire, faulty sender, etc.

Internal coolant leaks (coolant in oil, combustion gas bubbles in coolant ... either of which suggests a faulty head gasket, cracked head, or block).
Last edited by philip 13 years ago, edited 1 time in total.
-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"

after oil
Posts: 173
Joined: 13 years ago
Location: powell river, BC, Cascadia

#3

Post by after oil » 13 years ago

there were no visible or obvious leaks when i looked it over last night and this morning. there is coolant scattered hither and tither because the rad always surprises me when i open it!

now... i cant, unfortunatly, run the engine till i extract the broken bolt.
"... the rare and elusive 1987 D21/SD25, I have come to believe these trucks exist ONLY in the minds of people who own them. " phillip R.I.P.

1987 nissan d21 SD25, canada/2 tank SVO
1993 mitsubishi delica chamonix 4X4 diesel van

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philip
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#4

Post by philip » 13 years ago

after oil wrote:now... i cant, unfortunatly, run the engine till i extract the broken bolt.
Been there. I removed the entire housing to a machine shop having the wherewithall to cleanly melt out the bolt ... no thread repair required. $30.
-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"

after oil
Posts: 173
Joined: 13 years ago
Location: powell river, BC, Cascadia

#5

Post by after oil » 13 years ago

i checked the oil on the dipstick for signs of coolant, didnt seem like theres any. is there another way to know for sure?
"... the rare and elusive 1987 D21/SD25, I have come to believe these trucks exist ONLY in the minds of people who own them. " phillip R.I.P.

1987 nissan d21 SD25, canada/2 tank SVO
1993 mitsubishi delica chamonix 4X4 diesel van

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asavage
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#6

Post by asavage » 13 years ago

after oil wrote:there is coolant scattered hither and tither because the rad always surprises me when i open it!
You'll have to get out the garden hose and rinse everything down when you've got it all back together, as coolant has a very low evaporation rate and can take weeks to disappear at ambient temps.

Some of the symptoms you describe tally with an air lock: the water pump will not pump air. While the SD normally has no trouble purging air when initially filling the cooling system, your revised sig states you're running a two-tank SVO (WVO?) system, from which I may infer that you may have add'l coolant plumbing to heat the "fuel". If that's the case, you could have sizeable pockets of air in the "fuel" preheat system that, in normal operation, could move to the water pump area and cause an air lock.

Depending upon your preheat system, you might have to vacuum evacuate the cooling system to purge it of air. That's SOP for some newer vehicles that have portions of the cooling system above the highest purge point.

But that's only a guess: first, you'll have to deal with extracting or replacing the broken bolt(s) and removing all the external coolant, get it refilled and dried off, and see if you still have problems. You can't diagnose a disassembled system easily.

The SDs do not have a history of leakage at the head gasket area, even when overheated. All major components are cast iron and have considerable reserve thermal elasticity. The one exception is in the case of lack of cooling system maintenance (ie never changing the coolant, most of which -- green coolants especially -- have corrosion inhibitors that are only good for two years). If you run the same coolant for four, five or even more years, corrosion will happen, and the head gasket interfaces are vulnerable.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

after oil
Posts: 173
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#7

Post by after oil » 13 years ago

i hesitated to announce that i got a conversion, al, because i know your opinion of wvo :?
glad i did though, the highest part of the heating line for the wvo is about equal to the highest heater hose.

i replaced the thermostat, gasket (i could only find one that matched the coolant hole, but had to make new holes for the bolts to fit, it seals up fine)

i ran it for a while. after several minutes the thermometer read H.
whenever i gave it some juice some steam would appear, but i cant seem to find the source of it!


now... the engine was not hot. some hoses were hot, others were not hot. the rad had hot and cold spots, some even frigid!

the lines to the wvo heater were not hot.

vacuum evacuate the cooling system to purge it of air.
how do i do this?
"... the rare and elusive 1987 D21/SD25, I have come to believe these trucks exist ONLY in the minds of people who own them. " phillip R.I.P.

1987 nissan d21 SD25, canada/2 tank SVO
1993 mitsubishi delica chamonix 4X4 diesel van

after oil
Posts: 173
Joined: 13 years ago
Location: powell river, BC, Cascadia

#8

Post by after oil » 13 years ago

:D
i think i may be fine now! a friend came over and we checked some connections in the cooling system and got some air to burp out.
hopefully this is it.
thanks al, thanks phil
"... the rare and elusive 1987 D21/SD25, I have come to believe these trucks exist ONLY in the minds of people who own them. " phillip R.I.P.

1987 nissan d21 SD25, canada/2 tank SVO
1993 mitsubishi delica chamonix 4X4 diesel van

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philip
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#9

Post by philip » 13 years ago

after oil wrote::D
i think i may be fine now! a friend came over and we checked some connections in the cooling system and got some air to burp out.
hopefully this is it.
thanks al, thanks phil
Ahem ....
About that radiator with hot and cold spots. Now that you have (hopefully) all the air purged, recheck that radiator core. If it still has these hot/cool spots then coolant flow is choked off (cold areas), new core needed.
-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"

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asavage
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#10

Post by asavage » 13 years ago

after oil wrote:the lines to the wvo heater were not hot.
Big clue. Not hot = not circulating.

Sounds like you were able to purge enough air to get some consistent water flow. Good! I'll answer this anyway, though:
asavage wrote:vacuum evacuate the cooling system to purge it of air.
after oil wrote:how do i do this?
There is a vacuum generator for cooling systems that runs off compressed air. It's one of those venturi things. Works quite well, but it's not cheap. I used to use one at the shop where I worked. I had a manual that detailed the varying cooling system refill/purge procedures, and many cars that had low radiators and no bleed valve had to use it.

The idea is that you draw a vacuum on the cooling system, then let the vacuum suck fresh coolant in. Sounds flaky, but you get about 80-90% of the air out immediately that way.

It sounds like you were able to remove one of the WVO preheating hoses and purge air from the preheat circuit that way. That's a lot cheaper, though you don't want to spill a lot of expensive and toxic coolant.

You don't have to get all the air out manually, just enough that the centrifugal water pump can keep some water in it, so it can move coolant. No coolant in WP = no coolant flow, period (excluding thermosiphon effects, which won't work if you have air in the system either).

HTH
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.

after oil
Posts: 173
Joined: 13 years ago
Location: powell river, BC, Cascadia

#11

Post by after oil » 13 years ago

About that radiator with hot and cold spots. Now that you have (hopefully) all the air purged, recheck that radiator core. If it still has these hot/cool spots then coolant flow is choked off (cold areas), new core needed.
i test drove today again,on a full rad .the temp gauge got H then cooled a little.

some hoses were hot, the VO heater hoses were warm and the rad was cool.

the fluid level dropped
"... the rare and elusive 1987 D21/SD25, I have come to believe these trucks exist ONLY in the minds of people who own them. " phillip R.I.P.

1987 nissan d21 SD25, canada/2 tank SVO
1993 mitsubishi delica chamonix 4X4 diesel van

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kassim503
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#12

Post by kassim503 » 13 years ago

sounds to me like you are still burping air out of the system, if my quick scanning across the post is correct, you are running wvo with some long heater hoses that run far far down, it might take the motor a little while to blow all the air out of those lines if they arent self bleeding
'83 maxima sedan, l24e, a/t, black

227K SOLD 6/7/2012

after oil
Posts: 173
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Location: powell river, BC, Cascadia

#13

Post by after oil » 13 years ago

ya, theres a few feet of 1/4" line wrapped around the veg filter
"... the rare and elusive 1987 D21/SD25, I have come to believe these trucks exist ONLY in the minds of people who own them. " phillip R.I.P.

1987 nissan d21 SD25, canada/2 tank SVO
1993 mitsubishi delica chamonix 4X4 diesel van

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philip
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Location: Southern California, USA

#14

Post by philip » 13 years ago

after oil wrote:[ i test drove today again,on a full rad .the temp gauge got H then cooled a little. some hoses were hot, the VO heater hoses were warm and the rad was cool. the fluid level dropped
Seems like no two of these SVO preheat systems are plumbed alike so ... let me float some general principles.

Plumbing in parallel promotes air locks.

From a low mounted heat exchanger, coolant needs to exit at the high point of the device to be self purging of air. Notice how the engine oil heat exchanger is plumbed. The hose(es) are coolant exits.

The short / large diameter bypass hose (thermostat housing to water pump inlet) is a low resistance path compared to anything using the heater circuit. This all changes once the thermostat closes off the bypass near operating temperature. SO .... one could put a restriction into the bypass to force more coolant to flow through the heater circuit. Of course coolant flow through the heater itself is still controlled by the regulating valve.
-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"

after oil
Posts: 173
Joined: 13 years ago
Location: powell river, BC, Cascadia

things seem okay now, miraculously

#15

Post by after oil » 13 years ago

maybe ill post pictures tomorrow of the wvo heating system.
in short i plumbed a hose off the to-the-heater hose, through my heat exchangers, and then to the from-the-heater hose.

this morning i brought the truck to a rad shop where the coolant was tested for combustion emissions, seems there arent any.

pressure tested for leaks, none.

he said the few visible lines in the rad were not plugged

then to a shop that has the venturi thing vacuum purge. dude couldnt get the drain plug to open and didnt want to break it. he tried the vacuum anyway, for a split second, and it just sprayed fluid.

i made an appt. to have them remove the lower rad hose to drain it and then vacuum.

but after driving around a little more, the temp gauge was acting like it should. i checked under the hood, and everything seemed hot where it should be hot, no cold spots!

so i drove on petro-diesel, and wvo for 30km, no more problem.

:?

i canceled the appt. to purge the system, for now.
"... the rare and elusive 1987 D21/SD25, I have come to believe these trucks exist ONLY in the minds of people who own them. " phillip R.I.P.

1987 nissan d21 SD25, canada/2 tank SVO
1993 mitsubishi delica chamonix 4X4 diesel van

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